Grass:
* As green as: emerald, a freshly mowed lawn, a field of clover, a spring meadow
* As soft as: velvet, a baby's skin, a feather, a summer breeze
* As wild as: a jungle, a tangled forest, a untamed mane
Snow:
* As white as: a dove, a sheet, cotton, a winter sky
* As cold as: ice, a polar bear's nose, a frozen lake, a winter night
* As silent as: a whisper, a snowfall, a tomb, a ghost
Mist:
* As thick as: pea soup, fog, a blanket, a cloud
* As ethereal as: a dream, a ghost, smoke, a wisp of air
* As mysterious as: a fog-shrouded forest, a secret, a hidden treasure
Fear:
* As cold as: ice, a snake's gaze, a winter wind, a haunted house
* As heavy as: a weight on your chest, a burden, a stone, a dark cloud
* As sharp as: a knife, a thorn, a scream, a sudden shock
You can choose the simile that best fits the context and the tone you want to convey.